A major concern in manufacture electronic circuitry is the expansion and contraction of circuit components which can result as those components heated up and cooled down during operation. Today is not uncommon for an individual integrated circuit to give off as much heat as a 100 watt light bulb. Thus it can be seen that dealing with such heat is a major concern in circuit design. Not only must materials out of which circuits are manufactured be capable of handling the temperatures created in such circuitry, but they must also be capable of handling the pressures due to expansion and contraction caused by such heating and cooling.
Unfortunately many of the materials used to manufacture integrated circuits are not as good at handling these pressures as could be desired. For example, polyimide, a commonly used dielectric in the manufacture of integrated circuits and multichip modules is rather brittle once it has been cured (i.e., hardened). Attempts have been made to manufacture multichip modules using polyimide as the material to support conductive leads between individual integrated circuits contained in such modules. In the past such modules have failed as a result of the inability of polyimide to handle thermal expansion and contraction without cracking.
On large integrated circuits pressures due to thermal expansion contraction can also cause problems for the inflexible dielectric materials such as polyimide.
Thermal expansion and contraction can also create problems for many traditional methods of mounting integrated circuits upon printed circuit boards or multichip module substrates. Because integrated circuit normally have substrates made of different material than the substrate on which they are mounted, and because such chips often generate much more heat than substrate on which they are mounted, such chips often expand or contract in a different rate than their mounting substrate. For example, when chips are mounted upon rigid substrate using ball grid mounting, the pressure which the solder balls used in such mountings have to bear is often huge. In fact, on some occasions enough to break the solder connections holding such chips to their substrate.
Thus it can be seen that would be advantageous to develop methods of interconnecting electrical circuitry that has a greater capability to deal with the pressures due to thermal expansion and contraction.